A push-pull DC/DC converter converts an input DC voltage into an output DC voltage. The converter includes a transformer having a primary winding and a secondary winding. The windings are both wound around a common magnetic core. First and second switches alternately connect respective primary winding segments with a DC input source. The switches operate in opposite phase and conduct current through the corresponding primary winding segments during alternative half cycles. The output of the converter is regulated using duty control of the switches. The primary winding transfers energy to the secondary winding, which develops an alternating output that is rectified and filtered to provide a DC output.
Such a push-pull converter uses the magnetic core (i.e., the transformer core) over its entire magnetization curve, producing flux in the core having both positive and negative values. An issue is that the core may “walk” into saturation. Saturation of the core results from a net DC voltage being applied to the primary winding due to a net difference in the volt-second product of each half-cycle. This difference is typically caused by asymmetry in the operation of the switches due to delays in the various steps of amplification in the converter.
Open loop, push-pull DC/DC converters are susceptible to transformer core flux walk due to volt-second mismatch on the primary side of the converter. Once flux walking occurs the core saturates, which may cause increased primary currents, increased ringing and noise, damaged output diode rectifiers, and/or damaged switches.